Britney Lizama-Manibusan, Ph.D.
Department: Neuroscience, 2018
Faculty Mentor: BethAnn McLaughlin, Ph.D.
Dissertation Title: Novel Functions of C-terminus of HSC70-Interacting Protein (CHIP) in Mitophagy and Neuroprotection
Dissertation Abstract: C-terminus of HSC70-interacting protein (CHIP, STUB1) is a ubiquitously expressed cytosolic E3-ubiquitin ligase. CHIP-deficient mice exhibit cardiovascular stress and motor dysfunction prior to premature death. This phenotype is more consistent with animal models in which master regulators of autophagy are affected rather than with the mild phenotype of classic E3-ubiquitin ligase mutants. The cellular and biochemical events that contribute to neurodegeneration and premature aging in CHIP KO models remain poorly understood. Electron and fluorescent microscopy demonstrates that CHIP deficiency is associated with greater numbers of mitochondria, but these organelles are swollen and misshapen. Acute bioenergetic stress triggers CHIP induction and re-localization to mitochondria where it plays a role in the removal of damaged organelles. This mitochondrial clearance is required for protection following low-level bioenergetic stress in neurons. CHIP expression overlaps with stabilization of the redox stress sensor PTEN-inducible kinase 1 (PINK1) and is associated with increased LC3-mediated mitophagy. Introducing human promoter-driven vectors with mutations in either the E3 ligase or TPR domains of CHIP in primary neurons derived from CHIP-null animals enhances CHIP accumulation at mitochondria. Exposure to autophagy inhibitors suggests the increase in mitochondrial CHIP is likely due to diminished clearance of these CHIP-tagged organelles. Proteomic analysis of WT and CHIP KO mouse brains from both sexes reveals proteins essential for maintaining energetic, redox and mitochondrial homeostasis undergo significant changes in expression dependent upon genotype. Together these data support the use of CHIP deficient animals as a predictive model of age-related degeneration with selective neuronal proteotoxicity and mitochondrial failure.